DESCRIPTION OF PRIOR ART Such a device is known from US-A-50 82 067. One embodiment in that document includes a working chamber between two relatively movable parts, each with a channel or conduit for supply or discharge of pressure-fluid drive medium, appropriately compressed air. An. axial movement of a tubular upright displaces the valve element from its seat, thereby opening a fluid path to supply drive medium into the working chamber.

Pressurising the working chamber displaces the movable parts in mutually opposite directions, and when the movable parts have been sufficiently separated, the supply channel closes and the discharge channel in the upright opens for discharge of the drive medium allowing the relatively movable parts to approach each other so as to repeat the procedure described above. A reciprocating movement is obtained by using a system of springs or other means to return the parts towards each other after depressurisation.

Using the described embodiment would be very useful in an arrangement where the two movable parts are mutually discrete and disposed one after the other in the same housing. This arrangement would be very attractive as the tool diameter can

be made smaller and it therefore should provide for tools, which are easier to handle, have less demands on tolerances, have lower manufacturing cost, have less number of bearing surfaces and thus lower vibration level. However, a device built in the described manner has an effective output, which is too low to be of any practical use.

AIM AND MOST IMPORTANT FEATURE OF THE INVENTION It is an aim of this invention to provide a solution to the problems of the prior art and to suggest a solution making it possible to achieve better effective output while maintaining the advantages of the prior art.

It is a further aim to provide a solution allowing dimensional advantages and simple and economic manufacture because of the possibility of obtaining a device having reduced dimensions with maintained performance, compared to prior art. It is still a further aim to make these improvements useful for devices working as pneumatic tools including systems for vibration reduction.

These aims are achieved according to the invention through the features of claim 1. Corresponding aims are achieved through the other independent claims.

By positioning the fluid inlet to the working chamber separated from the fluid discharge, several advantages are achieved. The positions and dimensions of the inlet and discharge are independent of each other. Thus, each one can be independently optimised to suit the function and flow characteristics desirable for the specific application for which the device is to be applied.

By the valve elements being movable relative to the parts, several advantages are obtained such as self-adjustment of the valve arrangement. This in turn makes the arrangement relatively insensitive to tolerances, which allows economic manufacture.

According to a particularly preferred aspect, the valve elements are connected to each other by control means, (e. g. a stem) so as to form a valve body. This provides for excellent self-adjustment properties.

By allowing the valve elements to perform a limited movement relative to each other during operation, the operating cycle may be further optimised. This possibility provides for advantageous control of the operating cycle and thus enhanced performance. For example, the period when pressure-fluid is active inside the working chamber prior to discharge can be prolonged.

This function may be obtained by the connection between the valve elements being elastically flexible. The operating cycle can also be advantageously altered by at least one of the valve elements being flexible. A corresponding functional advantage is achieved by instead having at least one of the valve seats being elastically flexible.

The fluid pressure may also act on one or both of the valve elements to ensure that the element or elements is or are in the intended position or positions to perform the desired function.

Placing the two movable parts in a common housing in such a way that they are mutually discrete and disposed one after the

other and each part is sealing against the housing, makes it possible not only to build devices with smaller diameters, but also with smaller sealing surfaces and a lesser number of bearing surfaces. This tends to lower manufacturing costs and influence several other important variables positively and produce more power and lower noise and vibration level.

Further advantages are achieved through the features of the other dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail with reference to the annexed drawings, wherein Fig. 1 shows, in an axial section, a device according to the invention in a first. position, Figs. 2 and 3 show, in axial sections and in enlarged scale, the valve arrangement in different positions, Fig. 4 shows, in an axial section, a second embodiment of the invention, and Fig. 5 shows, in an axial section, a third embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS In this description like elements in different embodiments may carry the same reference signs.

In Fig. 1 reference sign 1 refers to a pressure-fluid driven device for generating a reciprocating movement. The device includes a housing 2, which encloses a first movable part 5

having a first channel or a fluid passage 6. Also a second movable part 3 is enclosed inside the housing 2. The part 3 is designed with an integral part 4 (in this case a stylus, but other designs with files, knives, saws, chisels etc. may also be used or it can be a piston hitting on a chisel, anvil, needles or similar) for performing some operation on a work piece (not shown). The movable parts delimit a working chamber 7 together with the housing 2.

The device may be adapted for generating a reciprocating movement, which can be used also for other applications involving driving members intended for reciprocation.

Pressure-fluid from a pressure-fluid source (not shown) is let into the housing 2 over an inlet 14 and passes through the fluid passage 6 into the working chamber 7 and is discharged from this working chamber 7 over a second channel or a discharge passage 15 to an outlet. The outlet is in the case of the shown embodiment arranged as channels through the wall of the housing 2.

The pressure-fluid flow through the device 1 is controlled by a valve arrangement, which includes a valve body 8 having a first valve element 10, which co-operates with the first movable part 5 and a second valve element 9, which co-operates with the second movable part 3.

This is shown in greater detail in Figs. 2 and 3. Fig. 2 shows the position of the valve body 8 when the two movable parts are far away from each other and the discharge passage 15 is open. Fig. 2 shows in particular the first valve element 10 co-operating with a surface which is positioned on an upstream side of the first part 5, and comprising a first valve seat

13. The second valve element 9 co-operates with a second valve seat 12, which is provided on the second part 3 (Fig. 3).

This means that pressure in fluid coming from the pressure- fluid inlet 14 in Fig. 1 urges the first valve element 10 against the first valve seat 13 in the position as seen in Fig. 2. Similarly, the second valve element 9 is pressed, through fluid pressure, which is being present inside the working chamber 7, in a direction against the second valve seat 12, so as to close the passage from the working chamber into the discharge passage 15 as shown in Fig. 3.

Figs. 2 and 3 also show that the valve body 8 includes a control means, in this case a stem 11 for connecting the first and second valve elements 9'and 10, respectively. The valve elements are thus axially separated a chosen distance from each other. The stem. li is accordingly dimensioned so as to allow a chosen distance between the parts 3 and 5 in order to provide for separation of the inlet and outlet areas.

According to the invention this feature provides advantageous flow characteristics with respect to flow of fluid into as well as out from the working chamber without the respective flow being disturbed or restricted by elements belonging to the other one of the respective one of the inlet or outlet functions. The stem is rigid in the embodiment shown but may also be flexible, which will be discussed later. The construction with the valve elements and the control means being an integral unit, which is free, in such a way that both valve elements are movable with respect to the parts, is advantageous in that it allows self-adjustment and makes the device relatively insensitive to tolerances.

Further, in Fig. 1 it is shown that the first part 5 is associated with a first force accumulator, in this case a spring 18. This spring 18 is put under increased load as the first movable part is moving in a first direction, i. e. forward or to the right in Fig. 1.

As the pressure-fluid drive medium enters the working chamber 7 through the inlet channel 6 passed the valve element 10, the two parts 5,3 are driven in opposite directions, the first part 5 to the left in Fig. 1, under simultaneous decrease of the load on its associated spring, and the second part 3 to the right under simultaneous increase of the load on its associated force accumulator, in this case a spring 17. The total of the reaction forces which are applied by the two springs directly or indirectly to the housing 2 will therefore remain substantially constant through the entire movement. cycle, which lowers vibrations of the housing. Naturally other force accumulators than springs may be used, e. g. draft springs, bellows, gas springs, rubber hoses etc.

In the embodiment of fig 4, the valve elements are separated elements and the second valve element 9 is provided with a control means 20 in the form of a stem which is guided in the first part so as to allow a restricted movement relative thereto. For that purpose, opposite to the second valve element it is provided with an enlargement 21 which co- operates with holding elements in the first part 5 so as to prevent the control means from falling out from the first part 5. The control means 20 is arranged to urge a first valve element 23 into an open position when the working chamber 7 contracts, i. e. the parts approach each other, and to urge the second valve element 9 into an open position when the working chamber 7 expands, i. e. the parts move away from each other.

It should be noted that the construction described with respect of fig 4 may be inverted in the sense that the first valve element could be attached to the control means which in that case would be guided in the second part. The valve elements would then be affected similar to the above case.

In the embodiment of Fig. 5, an arrangement is shown which in. principle operates in the same manner as the arrangements shown in figs 1-3. However, a valve body 8"having valve elements 9 and 10'is provided with a conduit 24 which functions so as to provide pressure fluid communication between volumes (not shown) on either side of the parts 3 and 5. This is advantageous e. g. if high pressure fluid is used for clean blowing purposes, for keeping a tool (e. g. a chisel) in a specific, position, to reduce the force needed to open the valve for incoming fluid etc. In the shown embodiment, the valve body 8'has an. extension 25 with an enlargement 26 at its free end matching inside the channel 27, and serving for guiding and sealing purposes. Outgoing fluid is discharged through a discharge channel 28, which opens downstream the valve seat for the valve element 9'. The extension 24 and the enlargement 26 are however optional with respect to the principle of pressure fluid communication through the conduit 8'.

The invention may be modified within the scope of the annexed claims. The invention may also be applicable in virtually any equipment using reciprocating movement besides tools.

The operating cycle can be modified by generally arranging for allowing the valve elements to perform a relative movement between each other, e. g. by making the stem 11 flexible. The operating cycle can also be modified by using valve elements,

which provide flexible co-operation with the movable parts. A further way of modifying the operating cycle is to use valve reception means, such as seats, being flexible for offering flexible co-operation with the valve elements.

The valve arrangement can be made in many different ways including being comprised of sliding valve elements being positioned in the respective parts.

Either one of the movable parts may be used as an active working part, but both parts can also be used for performing the useful work. They can e. g. impact on different parts of an anvil.

The embodiment of Fig. 1 may be amended such that one of the parts is fixedly attached to a support structure. Thus, in this case only the other one of the parts is free to move. The housing may be separate from, integral with or fixed to any of the respective parts.

Instead of using compression springs to return the movable parts towards each other there are many other possibilities including using pressure-fluid from the pressure-fluid source.